Method for concentration of aqueous tetrahydrofuran solutions by extraction with aqueous alkali metal hydroxide

ABSTRACT

A method for producing anhydrous tetrahydrofuran from an aqueous solution of tetrahydrofuran which comprises contacting an aqueous solution of an alkali metal hydroxide with the aqueous solution of tetrahydrofuran to remove the water.

Kisaki et a1.

States Patent METHOD FOR CONCENTRATION OF AQUEOUS TETRAHYDROFURANSOLUTIONS BY EXTRACTION WITH AQUEOUS ALKALI METAL HYDRO InventorsAssignee:

Filed:

Appl. No

XIDE

; Hisashi Kisaki; Shunsuke Mabuchi; Toshikatsu Mizuno, all of Yamaguchi,Japan Toyo Soda Manufacturing Co., Ltd., Tsuno-gun, Yamaguchi-ken, JapanAug. 11, 1970 Foreign Application Priority Data Aug. 14,

US. Cl.

Int. Cl.

1969 Japan ..'.44/63840 203/43 .;.....c0sd s/02 Field of Search....203/l4, 37, 43, 53; 260/3461 1 Sept. 26, 1972 References CitedPrimary Examiner-Wilbur L. Bascomb, Jr. Attorney-Flynn & FrishaufABSTRACT A method for producing anhydrous tetrahydrofuran from anaqueous solution of tetrahydrofuran which comprises contacting anaqueous solution of an alkali metal hydroxide with the aqueous solutionof tetrahydrofuran to remove the water.

6 Claims, 1 Drawing Figure r Mixer-- Settler l3 /6 l /5 THF a 2\ 1EgiiAXFJGCIMS koi solghon [0 Solution THF Solution Contummg Water METHOD FORCONCENTRATHON OF AQUEOUS TETRAHYDROFURAN SOLUTIONS BY EXTRACTION WITHAQUEOUS ALKALH METAL HYDROXIDE This invention relates to a method ofconcentrating aqueous solutions of tetrahydrofuran.

The following methods are known for the separation of tetrahydrofuranfrom an aqueous solution of tetrahydrofuran.

1. Addition of a solid dehydrating agent such as, for example, potassiumhydroxide, sodium hydroxide, potassium carbonate or sodium carbonate,and subsequent distillation to'recover the tetrahydrofuran.

2. Addition of, for example, glycerin, toluene, xylene or n-heptane toan aqueous solution of tetrahydrofuran, followed by stirring andsubsequent settling. The upper tetrahydrofuran layer obtained by thisphasic separation is distilled to recover the tetrahydrofuran.

3. Heating of an aqueous solution of tetrahydrofuran with the additionof an entrainer of water such as carbon disulfide or ether to recoverthe tetrahydrofuran.

4. Distillation of an aqueous solution of tetrahydrofuran with a solventsuch as, for example, butanediol, glycerin or ethylene glycol to recoverthe tetrahydrofuran.

5. Removal of water fromanaqueous solution of tetrahydrofuran byextraction with a saturated aqueous solution of, for example, calciumchloride or magnesium chloride to recover the tetrahydrofuran.

However, those conventional methods have their characteristicdisadvantages which include unsatisfactory degrees of dehydration thatcan be obtained or the complexity "of the process attending to therecovery of the reagent used and of tetrahydrofuran from the reagent.

In the light of the fact that a mixture of tetrahydrofuran and water maybe easily separated by simple distil lation into water and an azeotropicmixture, the fundamental principle of recovering a high puritytetrahydrofuran is the separation of water from such an azeotropicmixture to obtain a solution of tetrahydrofuran whichv is moreconcentrated than the azeotropic composition. As a result of our studieson the liquidliquid equilibrium composition of tetrahydrofuran,

water and a third reagent and on water extraction velocities, we havefound that a quite improved result is obtained with the use of anaqueous solution of alkali metal hydroxide than by using the compound inthe form of a solid.

Thus, such an alkali metal hydroxide is substantially insoluble intetrahydrofuran, while tetrahydrofuran is slightly soluble in an aqueousphase containing 20 percent or more of an alkali metal hydroxide only toa concentration which may bedisregarded in the recovery oftetrahydrofuran. Furthermore, the residual water content of thetetrahydrofuran phase may be easily reduced to a value of 0.5 weightpercent or less which is far lower than the corresponding content of theazeotropic mixture at atmospheric pressure, (about 6 weight percent) Inother words, an aqueous solution of 30 percent or more alkaliof metalhydroxide concentration is almost comparable to the corresponding solidalkali so far as dehydration power in concerned.

In addition, when a solid alkali is employed, a considerable amount oftetrahydrofuran may be lost in the form of emulsion with dischargedliquid alkali.

Therefore, it is difficult to hold the loss to 1 percent of even whenthe settling time is 5 to 8 hours, the duration is commerciallyallowable.

When an alkali is used in liquid form, it is easy to restrict the lossto less than 0.1 percent during a settling time of 3 hours at themaximum.

What is noteworthy is that the lower the concentration of alkali, theshorter the time of reaching liquidliquidequilibrium. Furthermore, theadvantage of the present invention which utilizes a liquid alkali overthe conventional art involving the use of a solid alkali is at onceapparent when one refers to the relative ease of transportation of aliquid against the packing and charging of a solid material.

Furthermore, when a given amount of a dehydrating agent is permitted toact upon an aqueous solution of tetrahydrofuran for a given time, it isclear that the use of a liquid reagent is more advantageous than the useof a solid reagent in terms of contact area, state of dispersion, easeof contact and other aspects.

Stated differently, to achieve a given degree of dehydration, the amountof the extractant required is smaller when it is a liquid.

In the extraction of water with an aqueous solution of a salt such as,for example, calcium chloride, magnesium chloride or potassiumcarbonate, it is impossible to reduce the water content of thetetrahydrofuran layer to less than 1.5 percent even with the use of asaturated solution. The increase in residual water content is aneconomical disadvantage, for it represents an increased volume ofcirculation through an azeotropic dehydration still.

in accordance with one embodiment of this invention, it is convenient toemploy an extractor in conjunction with a settling vessel, and the flowsof aqueous tetrahydrofuran and the aqueous alkali solution may be eitherparallel or countercurrent.

An example will be shown in which a 48 percent aqueous solution ofsodium hydroxide is used for the recovery of a mixture of 99.5 percenttetrahydrofuran and 0.5 percent water on the basis of the ternaryequilibrium.

In this example, it is sufficient to employ a one-stage extractor whenthe expected alkali concentration of the exit solution is 40 percent orhigher, a two-stage extractor when the exit alkali concentration is 30percent and a four-stage extractor when the concentration is 20 percent.The concentration of alkali metal hydroxide in the tetrahydrofuran phaseis less than 0.1 ppm, and the concentration of tetrahydrofuran in theaqueous alkali solution phase is 0.6 to 0.7 percent (alkaliconcentration of exit solution is 20 percent), 0.08 to 0.1 percent30percent) or 0.01 to 0.02 percent( 40 percent).

The upper limit of alkali concentration is about 50 to percent underatmospheric pressure and ordinary temperature. However, at an elevatedpressure and elevated temperature, the alkali concentration may behigher, though the use of pressure vessels would be insensible,costwise.

Of the two liquid phases obtained on standing after a sufficientcontacting time, the tetrahydrofuran layer is fed into a distillationcolumn or still for complete dehydration, wherein an azeotropic mixtureof water and tetrahydrofuran is obtained at the top of the column andanhydrous tetrahydrofuran at the bottom. The aqueous alkali layer may,if required, be trans ferred to a tetrahydrofuran recovery step and, ifneces sary, to a concentration means, but the recovery oftetrahydrofuran from this phase is generally unnecessary if a suitableexit concentration is selected.

The following examples are further illustrative of this invention.

EXAMPLE 1 A glass extractor equipped with a stirrer was continuously fedwith varying proportions of tetrahydrofuran containing 6 percent waterand of a 48 percent aqueous solution of sodium hydroxide. The twomaterials were vigorously stirred. The mixture was then allowed toseparate into two layers in a settling vessel. The average residencetime of the sodium hydroxide in the settling vessel was 180 minutes.

The results are summarized below.

THF (6% water)(parts) I I00 I00 I00 48% sodium hydroxidefinch) 50 l7 l06 Water content of 0.35 0.54 0.83 1.4

Loss of THF (36) 0.0 l 0.005 0.001 0.01

EXAMPLE 2 A glass extractor equipped with a stirrer was continuously fedwith varying proportions of tetrahydrofuran containing 6 percent waterand a 35 percent aqueous solution of sodium hydroxide. After thematerials were vigorously stirred, the mixture was separated into twolayers in a settling vessel.

The average residence time of the sodium hydroxide in the settlingvessel was 180 minutes. The conditions and results are as set forthbelow.

THF 6% waterflparts) I00 100 I00 35% sodium hydroxidefinch) I00 50 I5Water content ofTHF (76) 0.9 1.3 2.4

Loss of THF (96) 0.03 0.005 0.02

EXAMPLE 3 A glass extractor equipped with a stirrer was continuouslysupplied with 100 parts tetrahydrofuran containing 70 percent water and50 parts of 48 percent aqueous solution of sodium hydroxide. Afterthorough mixing, the mixture was allowed to separate into two layers ina settling vessel.

The average residence time of the sodium hydroxide in the settlingvessel was 60 minutes. The water content of the product tetrahydrofuranwas 4.7 percent and the sodium hydroxide content of the same was notsufficient to be positive to phenolphthalein. The concentration ofsodium hydroxide in the exit solution was 20.l percent and thetetrahydrofuran content thereof was 0.6 percent.

The percent recovery of tetrahydrofuran was 97.7 percent.

EXAMPLE 4 One-hundred parts tetrahydrofuran containing 6 percent waterand 40 parts of 51.6 percent aqueous solution of potassium hydroxidewere continuously fed to a glass extractor equipped with a stirrer andafter thorough mixing, the mixture was allowed to separate into twolayers in a settling vessel. The average residence time of the potassiumhydroxide in the settling vessel was minutes. The water content of thetetrahydrofuran layer was 0.4 percent, and the potassium hydroxidecontent of the same layer was not sufficient to be positive tophenolphthalein.

The potassium hydroxide concentration of the exit solution was 45percent and the tetrahydrofuran content of the same solution was 0.4percent.

The percent recovery of tetrahydrofuran was 99.8 percent.

The invention can be carried out in typical apparatus as shown in thedrawing. Aqueous THF is charged through line 10 to mixing vessel 11 withan aqueous alkali hydroxide solution charged through line 12. Vessel 11is equipped with an agitator (not shown). The resulting mixture formedin vessel 11 is discharged into settler 13, which is preferably equippedwith baffle 14. Aqueous alkali solution is withdrawn from settler 13through line 15, and THF containing substantially less water than inline 10 is discharged from 13 through line 16. Vessel 11 can be equippedwith valved vent line 17.

We claim:

1. A method for removing water from aqueous solution (1) hydroxidetetrahydrofuran, which comprises contacting an aqueous solution (2) ofan alkali metal hydroxide with said aqueous solution l) oftetrahydrofuran, whereupon water is extracted from solution (1) bysolution (2), and recovering tetrahydrofuran (3) having a substantiallylower water content than said solution l), the alkali metal hydroxideconcentration of said aqueous alkali metal hydroxide solution being from30 to 60 weight percent.

2. A method according to claim I, wherein said alkali metal hydroxide isselected from the group consisting of sodium hydroxide and potassiumhydroxide.

3. A method according to claim 1, wherein the concentration of saidalkali metal hydroxide in the resulting residual phase after recovery ofthe tetrahydrofuran water mixture is more than 20 percent.

4. A method according to claim 1, wherein said tetrahydrofuran (3) isdistilled in a distillation vessel, an azeotropic mixture of water andtetrahydrofuran is removed as an overhead fraction from said vessel, andsubstantially anhydrous tetrahydrofuran is removed as bottoms fractionfrom said vessel.

5. A method according to claim 4, wherein said alkali metal hydroxide isselected from the group consisting of sodium hydroxide and potassiumhydroxide.

6. A method according to claim 4, wherein the concentration of saidalkali metal hydroxide in the resulting residual phase after recovery ofthe tetrahydrofuran water mixture is more than 20 percent.

2. A method according to claim 1, wherein said alkali metal hydroxide isselected from the group consisting of sodium hydroxide and potassiumhydroxide.
 3. A method according to claim 1, wherein the concentrationof said alkali metal hydroxide in the resulting residual phase afterrecovery of the tetrahydrofuran water mixture is more than 20 percent.4. A method according to claim 1, wherein said tetrahydrofuran (3) isdistilled in a distillation vessel, an azeotropic mixture of water andtetrahydrofuran is removed as an overhead fraction from said vessel, andsubstantially anhydrous tetrahydrofuran is removed as bottoms fractionfrom said vessel.
 5. A method according to claim 4, wherein said alkalimetal hydroxide is selected from the group consisting of sodiumhydroxide and potassium hydroxide.
 6. A method according to claim 4,wherein the concentration of said alkali metal hydroxide in theresulting residual phase after recovery of the tetrahydrofuran watermixture is more than 20 percent.